Target structure for image transducer



Nov. 15, 1960 .1. E. JACOBS TARGET STRUCTURE FOR IMAGE TRANsDUcER Filed Aug. 19, 1957 NOE INVENTOR- JOHN E. JACOBS ATTO RN EY T T T r? United States Patent TARGET STRUCTURE FOR lll/[AGE TRANSDUCER Jolm E. Jacobs, Hales Comers, Wis., assignor to General Electric Company, a corporation of New York Filed Aug. 19, 1957, Ser. No. 67 8,796

A7 Claims. (Cl. 313-65) The present invention relates in general to rayborne image transducers or iconoscopes, and has more particular reference to an improved image transducing target structure for iconoscopes.

As shown, for example, in copending applications for U.S. Letters Patent, Serial No. 357,222, of May 25, 1953, now U.S. Patent No. 2,951,898; Serial No. 418,414, of March 24, 1954, now U.S. Patent No. 2,809,323; Serial Number 518,884, of June 29, 1955, now U.S. Patent 2,890,360; and Serial No. 538,846, of October 6, 1955, now U.S. Patent No. 2,889,188, on the inventions of John E. Jacobs as sole inventor, and as joint inventor with Harold Berger, latent picture images, especially images latently carried by penetrating rays, such as X-rays, may be transduced or converted into electrical impulses for the operation of conventional picture reproducing tubes of the sort commonly employed in television apparatus. Latent ray carried images may thus be transduced by applying the image bearing rays upon a transducing layer comprising a suitable photosensitive semiconductor material, while continuously and repetitively scanning the transducing layer in order to provide an electrical signal corresponding with the latent image vthus applied upon the layer and adapted for the operation of a picture reproducing tube.

An important object of the present invention is to provide an improved transducing layer forming'a ltarget structure for receiving the impingement thereon of latent picture carrying rays, the improved target structure avoiding ray absorbing characteristics inherent to target structures of the sort heretofore provided. l

Another important object is to provide a ray carried image transducing target structure incorporating a bucky diaphragm characteristic whereby the definition and clarity of the transduced image is improved through the '-elimination'of the eiects of picture quality impairing secondary radiation which may be present in the image carrying rays.

Another important object of the invention is to provide a target structure for rayborne image transducers comprising a foraminous support panel of electrical conducting material carrying a layer of ray sensitive semiconductormaterial in position to receive the impingement of image carrying rays; a further object being to employ a preferably stainless steel wire mesh screen as a layer carrying support panel; a still further object being to employ a foraminous support panel in which the diametral dimension of the openings is substantially equal to the maximum thickness of the panel supported layer of photosensitive material; still another object of the 'invention is to employ a foraminous support panel formed with openings having a diametral dimension of 'the order of 0.01 inch; yet another object being to form a layer having maximum thickness in registration with the openings of the foraminous supporting panel; still Yanother object being to employ lead monoxide (PbO),

i Briey stated, the present invention provides an image v 'transducer embodying a target structure comprising a Patented Nov. 15,196.0

iflee stainless steel wire mesh screen forming a support panel carrying a layer of lead monoxide, the same being a semiconductor sensitive to penetrating rays, such as X-rays, said target structure being adapted for enclosure in a sealed, preferably evacuated envelope, in position to receive the impingement of latent image carrying rays applied upon one side of said layer, means being provided to scan the layer progressively and repetitively with an electron beam through a foraminous, preferably wire mesh grid disposed in spaced, preferably parallel relationship with respect to the photosensitive layer of semiconductive material, to thereby develop an Velectrical signal corresponding with the latent picture image applied in said layer by said rays, as seen by the scanning beam.

The foregoing and numerous other important objects, a-dvantages and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection with the accompanying drawings, discloses a preferred embodiment of the invention.

Referring to the drawings:

Fig. 1 is a sectional view through an image transducer comprising a target structure embodying the present invention;

Fig. 2 is a greatly enlarged fragmentary sectional view taken substantially along the line 2-2 in Fig. l; and

Figs. 3 and 4 are diagrammatic sectional views through the target structure.

To illustrate the invention, the drawings show an image transducer or iconoscope 11 adapted to receive penetrating rays 12, such as X-rays, emanating from a suitable ray source and latently carrying the image of an object 13, disposed in the path of the rays 12 between the ray source and the transducer 11. The transducer 11 is generally of the sort forming the subject matter of the above mentioned applications for U.S. Letters Patent, the same being adapted to produce electrical signal impulses corresponding with the characteristics of the image latently carried by the rays 12. Signal impulses produced by the transducer may be delivered to and applied for the operation of a remotely located picture ray producing tube, of the sort commonly employed in television apparatus.

As shown, the transducer 11 may comprise a sealed and evacuated envelope 14, preferably formed of glass and providing a tubular electron gun housing 15 at one end of the envelope, and an enlarged envelope portion 16 forming a scanning chamber in open communication with the gun housing, at one end thereof. The envelope 14 may include a preferably outwardly bowed end wall 17 sealing and enclosing the end of the scanning chamber remote from and opposite the gun housing. Latent image pickup -means 18 is provided within the end wall 17 in postion to be disposed in the path of the image carrying rays 12, said pickup means being also disposed in alinement with the gun housing, in position to be scanned by an electron beam 19 emitted by an electron gun structure 20 mounted in the gun housing.

The gun structure 20 may be of any suitable, preferred or convenient form, and may be used in connection with conventional horizontal and vertical beam dellecting plates 21; or conventional magnetic beam deflecting coils disposed outwardly of the gun housing may be employed in conjunction with the gun for beam deecting'purposes, in accordance with well known electron scanning beam procedures. The image pickup means 18, in accordance with the present invention, comprises a relatively thin layer of photosensitive semi-conducting material 22, such as lead monoxide (PbO), said layer being coated upon and in electrical contact with a foraminous support panel 23 of electrical conducting material.

As shown, the support panel 23 comprises a woven mesh screen, preferably formed of stainless steel Wire, upon which the layer of semi-conducting material 22 is carried. Irradiation of the layer 22 by image carrying rays 12 will correspondingly alter the impedance of the material of the layer and ythus apply, in the layer 22, a latent image correspondingly with the ray carried image to be transduced, said layer image being defined in the layer 22 in terms of the impedance characteristics of each integral portion of the irradiated layer. The transducer 11 thus provides means for successively and repetitively measuring the ray controlled condition of each integral portion of the layer 22, to thereby produce transmissable signals corresponding with the latent image applied in the layer 22. To these ends, the pickup means 18, in addition to the layer 22 and its foraminous support panel 23, may comprise a foraminous screen 24 mounted in closely spaced, preferably parallel relationship with respect to the layer 22.

The foraminous screen 24 may comprise a tine mesh woven metal wire screen, of the order of sixty meshes per lineal inch, the foraminous target supporting panel 23 and the wire mesh screen 24 being electrically insulated, the one from the other, and being supported in spaced relation, such spacement being preferably of the order of one-eighth of an inch. The screen 24 may be tightly stretched and secured upon a suitable support frame 25 of electrical conducting material, the marginal edges of the screen being electrically and mechanically secured to the frame, as by means of solder.

The envelope 14 may embody reentrant envelope portions 26, 26', carrying stems '27, 27 of electrical conducting material forming glass-to-metal seals 28, 28 with said reentrant portions. The stems extend within the enlarged envelope portion 16 and terminate adjacent the end wall 17 of the envelope. The opposite ends of the stems may extend outwardly of the envelope through the reentrant portions thereof, said outwardly extending stem portions being electrically connected, as at 29, 29', with preferably flexible conductors 30, 30'. The screen carrying frame 25, as well as the layer supporting panel 23, may be mounted upon the stems 27, 27 in fashion presenting the panel and screen immediately inwardly of the envelope end wall 17, the screen 24 being disposed in parallel spaced relation with respect to the layer 22 and between it and the electron gun structure 20. The layer supporting panel 23 and the screen carrying frame 25 may be mounted upon the stems 27, 27 in fashion electrically connecting the panel only with one of the stems, such as the stem 27; and the frame 2'5 only with another of said stems, such as the stem 27', both the panel and frame being mechanically supported on all of the stems.

When the transducer is in operation, a potential difference of desired value, supplied from a suitable power source 31, may be maintained between the panel 23 and the foraminous screen 24. To this end, the power source 31 may be medially connected to ground, the opposite ends of the source being connected across a resistor 32, forming a potentiometer having an associated adjustable tap. This tap may be connected with the foraminous screen connected conductor 30 through a resistor 33. By adjusting the potentiometer tap, any desired positive or negative voltage, with respect to ground, Within the voltage supplied by the source 31, may be applied to the mesh screen 24. If desired, the screen may be connected to ground through a condenser 34; and the layer supporting panel 23 may also be connected to ground, as through the conductor 30 and an output resistor 35.

When the layer 22 is dark, that is to say, when it is not being irradiated by image carrying rays 12 to which it is responsive, the voltage drop across the layer 22, when the same is scanned by the electron beam 19, will be merely the small current loss Vcharacteristic of the constituent material `of the layer. When the layer is exposed to rays to which it is sensitive, the voltage drop across the layer will be directly proportional to the intensity of layer impinging rays. Such voltage drop, however, at the spot of impingement of the scanning beam 19, will be instantly restored from the power source 31, since the scanning beam 19 will serve as a conduction path between the foraminous screen 24 and the facing surface of the layer 22. The extent of such restoration may be measured in terms of a iluctuating voltage developed across the output resistor 35; and such uctuating voltage will accurately define the latent image imposed upon the layer 22 by the layer exciting rays 12, as seen by the scanning beam 19. The voltage developed across the resistor 35 may be applied through a coupling condenser 36 as a signal for controlling the operation of a remotely located picture reproducing tube of conventional character.

Heretofore, it has been customary to apply the photoconductive layer 22 upon a relatively thin imperforate plate of electrical conducting material through which the image carrying rays penetrate, in order to impinge upon the photoconductive layer. however, absorb up to forty percent of the energy of the image carrying rays, thereby appreciably impairing the action of the transducer. By arranging for the support of the semi-conductor image transducing layer 22 upon a foraminous support member 23, the undesirable vray absorbing effect encountered in targets embodying stainless steel support plates, is entirely eliminated. Indeedl devices embodying the present invention have ray sensitivity of the order of four times that of devices embodying targets comprising imperforate layer carrying plates. In addition, it has been found that the employment of a foraminous layer carrying member, in accordance with the present invention, incorporates bucky diaphragm characteristics in the target structure, thereby greatly improving definition in picture images transduced in devices embodying the present invention.

The photoconductive portions of the layer 22 that are employed in transducing images in accordance with the present invention, are those which extend vopposite the openings of the foraminous panel 23. The sizes of such openings, as indicated in Fig. 3 of the drawings, are preferably such that the electric field existing across the layer at such transducing portions thereof, are equal to or greater than that existing across the layer immediately behind the mesh wires. The Voltage gradient at E should exceed that at E2. This condition is most nearly obtained when the mesh openings are equal in dimension to the thickness of the layer of semi-conductor material, such being preferably of the order of 0.91 inch. Since the photo current in the layer is proportional to the intensity of the appplied electric eld, the sensitivity of the target will be substantially as shown in Fig. 4 of the drawings.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit and scope of the invention, or sacrificing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

l. A penetrating ray transducer comprising a foraminous support panel of electrically conducting material, and a layer of sensitive semi-conductor material anchored on said support in electrical contact therewith and extending across the openings in said layer and having thickness in register with said openings, substantially equal to the diametral dimension of the opening, s aid layer having an undulating surface of such nature that the thickness of said layer in register with an opening is less Such layer carrying plates,Y

than the layer thickness in register with the support dening the boundary of said opening.

2. A penetrating ray transducer comprising a foraminous support panel of electrical conducting material, and a layer of ray sensitive semi-conductor material supported on and in electrical contact with said panel in position to be exposed to penetrating rays to which the material of the layer is sensitive through the openings of the panel, said layer having varying thickness such that the voltage gradient from said panel across the layer portions opposite the panel openings exceeds the voltage gradient across the layer portions in registration with the panel material which defines said openings peripherally thereof, when the panel is connected to one polarity terminal of an external circuit and a moving electrode point connected to the other terminal of such circuit moves to scan the surface of said electrical conducting material.

3. A penetrating ray transducer comprising a foraminous support panel of electrical conducting material, and a layer of lead monoxide supported on and in electrical contact with said panel in position to be exposed to penetrating rays to which the material of the layer is sensitive as a semi-conductor through the openings of the foraminuous panel, said layer having thickness such that the voltage gradient from said panel across the layer portions opposite the panel openings exceeds the voltage gradient across the layer portions in registration with the panel material which denes said openings peripherally thereof, when the panel is connected to one polarity terminal of an external circuit and a moving electrode point connected to the other terminal of such circuit moves to scan the surface of said electrical conducting material.

4. A penetrating ray transducer comprising a foraminous support panel of electrical conducting material, and a layer of ray sensitive semi-conductor material supported on and in electrical contact with said panel in position to be exposed to penetrating rays to which the material of the layer is sensitive through the openings of the panel, said layer having thickness` such that the voltage gradient from said panel across the layer portions opposite the panel openings exceeds the voltage gradient `across the layer portions in registration with the panel material which denes said openings peripherally thereof, when the panel is connected to one polarity terminal of an external circuit and a moving electrode point connected to the other terminal of such circuit moves to scan the surface of said electrical conducting material, the layer of semi-conductor material having thickness of the order of the diametral dimension of the openings in the foraminous support panel.

5. A penetrating ray transducer comprising a Wire mesh of electrical conducting material, and a layer of ray sensitive semi-conductor material supported on and in electrical contact with said mesh in position to be eX- posed to penetrating rays to which the material of the layer is sensitive through the openings of the mesh, said layer having thickness such that the voltage gradient from said mesh across the layer portions opposite the mesh openings exceeds the voltage gradient across the layer portions in registration with the constituent Wires of said mesh, when the mesh is connected to one polarity terminal of an external circuit and a moving electrode point connected to the other terminal of such circuit moves to scan the surface of said electrical conducting material.

6. A penetrating ray transducer comprising a Wire mesh of electrical conducting material, and a layer of lead monoxide supported on and in electrical contact With said mesh in position to be exposed to penetrating rays to which the material of the layer is sensitive as a semiconductor through the openings of the mesh, said layer having thickness such that the voltage gradient between the Wires of the mesh across the layer portions opposite -the mesh openings exceeds the voltage gradient across the layer portions in registration with said constituent wires, when the mesh is connected to one polarity terminal of an external circuit and a moving electrode point connected to the other terminal of such circuit moves to scan the surface of said electrical conducting material.

7. A penetrating ray transducer comprising a wire mesh of electrical conducting material, and a layer of ray sensitive semi-conductor material supported on and in electrical contact with said mesh in position tobe exposed to penetrating rays to which the material of the layer is sensitive through the openings of the mesh, said layer having thickness such that the voltage gradient from said mesh across the layer portions opposite the mesh openings exceeds the voltage gradient across the layer portions in registration with the constituent wires of said mesh, When the mesh is connected to one polarity Y terminal of an external circuit and a moving electrode point connected to the other terminal of such circuit moves to scan the surface of said electrical conducting material, the layer of semi-conductor material having thickness of the order of the diametral dimension of the mesh openings.

References Cited in the le of this patent UNITED STATES PATENTS 2,739,243 Sheldon Mar. 20, 1956 2,809,323 Jacobs Oct. 8, 1957 FOREIGN PATENTS 485,496 Canada Aug. 5, 1952 1,064,426 France Dec. 23, 1953 165,963 Australia Nov. l0, 1955 

